The adult respiratory distress syndrome (ARDS) has been linked pathogenetically to the activation of complement and complement mediated neurophil deposition in the lung. We have described a series of patients with profound neutropenia who developed the clinical syndrome of ARDS. Pathologic studies obtained on half of these patients revealed classic pulmonary pathology for ARDS with no neutrophils present in the lung. This study indicates that the ARDS syndrome can occur in the absence of neutrophils. Other pathogenetic mechanisms without neutrophils must also be able to result in ARDS.